Polyurethane has been used widely in surface coating industry such as adhesive, ink, and colour coating. At present, water-based polyurethane dispersions (PUDs) are a rapidly growing segment of the polyurethane coating industry due to their versatility and environmentally friendly with zero to low volatile organic content (VOC). Moreover, the water-based polyurethane has low viscosity although the polymer chain itself has high molecular weight. This makes it available in a wide range of hardness and solid content for suitable formulation into a compliant coating on many different substrates. Polyurethane can be prepared from isocyanate and polyol compounds such as polyester polyol or polyether polyol, which can be prepared either from petroleum or bio-based source such as vegetable oil, starch, carbohydrate, or bio-based substances from fermentation process.
Polyester polyol can be prepared in many ways. One of interesting ways is the preparation from epoxidation of glyceride compound such as U.S. Pat. No. 7,629,478B2 disclosed a preparation process for polyester polyol for polyurethane production by epoxidizing monoglyceride, which obtained from reaction between unsaturated fatty acid or unsaturated triglyceride, with polyhydric alcohol. The resulting product was then reacted with polyhydric alcohol such as sucrose resulting in epoxide ring opening to obtain polyester polyol. The ratio of fatty acid or triglyceride to polyhydric alcohol was about 4 to 6 mole of polyhydric alcohol per mole of fatty acid or triglyceride. However, this patent document did not mention the relationship of polyester polyol and its suitable application. Different polyester polyol structure was suitable for the production of different types of polyurethane which could affect the properties of polyurethane.
Apart from monoglyceride, polyglyceride has been used for the preparation of polyester polyol. Polyglyceride can be prepared in many ways such as European patent publication no. EP0132941A1 disclosed the preparation method for polyglyceride with higher number of fatty acid chain by transesterification of polyol with fatty acid ester in the absence of solvent. Canadian patent publication no. CA2004723A1 mentioned polyglyceride obtained from transesterification of soil been oil and sugar with hydroxyl group. However, polyglyceride obtained from those patent documents were suitable to be used as emulsifier in food and medical applications because of low hydroxy group on their structures and its solid form at ambient temperature, which was not suitable for using in polyurethane production especially in coating applications. Therefore, the present invention focuses on polyester polyol composition from polyglyceride for the production of polyurethane dispersion which has not been disclosed so far.
In the preparation of polyurethane dispersion, normally internal emulsifier is added to provide ionic charge on polyurethane chain. The ionic charge, that a polymer molecule carries on it, needed to be controlled in an appropriate number to obtain polyurethane with high stability in aqueous media. However, it also depends on other parameters such as nature of polymer and neutralization rate between carboxylic acid and base functional groups. Internal emulsifier for the preparation of polyurethane dispersion such as dihydroxy fatty acid compound according to U.S. Pat. No. 5,512,655, or hydrophilic dihydroxy sulfonate monomer according to Chinese patent no. CN103232372, or 1,2-di-substituted oxyethylene according to patent publication no. US20120214938A1. Said internal emulsifiers need to be added into system during the preparation of polyurethane prepolymerization, which is complicated and need more steps in working process.